Yoshiaki Ohta

Controlling TCP ACK transmission for throughput improvement in LTE-Advanced Pro

The 3rd Generation Partnership Project (3GPP) is standardizing LTE-Advanced (LTE-A) Pro. One of the technical challenges is the reduction of the uplink latency, which is larger than the downlink latency, aiming at improving the Transmission Control Protocol (TCP) throughput. A study item called Latency Reduction (LATRED) has been agreed to standardize fast uplink access schemes. The proposed solutions include shortening of the subframe length and fast uplink resource allocation to mobile terminals for the uplink data transmissions. The reason for this is that speeding up the data processing of the layer 1 and the layer 2 protocols reduces the TCP Round Trip Time (RTT) and hence the downlink TCP throughput can be improved. However, the asymmetric bandwidth of the radio link has not been taken into account. The asymmetry tends to cause the uplink congestion and uplink resource shortage for TCP ACK transmission, which has a negative impact on the TCP RTT. In this paper, we propose methods to improve the TCP throughput focusing on the TCP ACK filtering in the LTE-A Pro uplink.

Link layer structure for LTE-WLAN aggregation in LTE-Advanced and 5G network

In LTE-Advanced (LTE-A), system enhancements have been studied in the 3GPP (3rd Generation Partnership Project) for standardizing integrated wireless communications using multiple radio access technologies (RATs) toward 5th generation (5G) mobile communications. One of study topics is LTE-WLAN (Wireless LAN) aggregation, aiming at enabling simultaneous usage of LTE radio access and WLAN radio access. An important technical challenge is the existing layer 2 structure. Specifically, the layer 2 structure for LTE-WLAN aggregation should be designed so that the Quality of Service (QoS) level of Evolved Packet System (EPS) bearers is kept even when each EPS bearer is sent over the WLAN radio. Requirements should include: (1) the layer 2 structure must be backward compatible to existing LTE-A specifications, and (2) the layer 2 structure must not have any impacts to existing WLAN specifications. In order to meet these requirements, in this paper, three layer 2 structures are proposed. The characteristics of proposed layer 2 structures are clarified, the pros and cons are discussed, and then one of proposed layer 2 structures is selected as a desirable structure to be standardized in 3GPP for LTE-WLAN aggregation.

Controlling TCP ACK transmission: Impact of discard ratio on performance in LTE-Advanced Pro

Recent research interest in cellular communication systems focuses on the design of the radio access networks (RAN) considering Transmission Control Protocol (TCP) behavior. However, less attention has been paid to the specific transmission method of TCP ACK. The authors have been studying methods including TCP ACK filtering that can well work with the link layer protocols in LTE-Advanced Pro (LTE-A Pro), where the TCP ACKs can be intentionally discarded. Basic methods of TCP ACK filtering have been investigated and it has been clarified that there is a method that can accomplish good TCP throughput with a reduced number of TCP ACKs. In this paper, we further study TCP ACK filtering and develop new methods, which are generalized methods of TCP ACK filtering. The novel feature of our new method is that the TCP ACK filtering can be controlled by a “discard ratio” parameter. The performance is evaluated by computer simulations. It is observed that the TCP throughput remains good even when the discard ratio is set to large values. In addition, it is found that there exists a value of the “discard ratio which can minimize the number of TCP ACKs while maintaining good TCP throughput.